however, i do have a question about pullups. is there a difference in effectiveness for big guys over skinny guys? i always see skinny guys with small backs easily ripping off a dozen or so pullups. in my opinion, based on my observation, the pullup is not effective for growing their lats.

I suppose that could be due to the relatively lower resistance afforded by their lower bodyweight. If that is so, instead of bodyweight pullups, may be weighted pull ups would be more useful for skinnier guys?